The present invention relates generally to scroll compressors and more specifically to a capacity modulation system of the delayed suction type for such compressors.
Refrigeration and air conditioning systems are commonly operated under a wide range of loading conditions due to changing environmental conditions. In order to effectively and efficiently accomplish the desired cooling under such changing conditions, it is desirable to incorporate means to vary the capacity of the compressors utilized in such systems.
A wide variety of systems have been developed in order to accomplish this capacity modulation most of which delay the initial sealing point of the moving fluid pockets defined by scroll members. In one form, such systems commonly employ a pair of vent passages communicating between suction pressure and the outermost pair of moving fluid pockets. Typically these passages open into the moving fluid pockets at a position normally within 360.degree. of the sealing point of the outer ends of the wraps. Some systems employ a separate valve member for each such vent passage which valves are intended to be operated simultaneously so as to ensure a pressure balance between the two fluid pockets. Other systems employ additional passages to place the two vent passages in fluid communication thereby enabling use of a single valve to control capacity modulation.
The first type of system mentioned above creates a possibility that the two valves may not operate simultaneously. For example, should one of the two valves fail, a pressure imbalance will be created between the two fluid pockets which will increase the stresses on the Oldham coupling thereby reducing the life of the compressor. Further, such pressure imbalance may result in increasing operating noise to an unacceptable level. Even slight differences in the speed of operation between the two valves can result in objectionable noise generating transient pressure imbalances.
While the second type of system mentioned above eliminates the concern over pressure imbalances encountered with the first system, it requires additional costly machining to provide a linking passage across the scroll end plate to interconnect the two vent passages. Additionally, the addition of this linking passage increases the re-expansion volume of the compressor when it is operated in a full capacity mode thus reducing its efficiency.
The present invention, however, overcomes these and other problems by providing a single valving ring operated by a single actuator so as to ensure simultaneous opening and closing of the vent passages thus avoiding any possibility of even transient pressure imbalances in the fluid pockets. In one embodiment, the valving ring of the present invention is in the form of an annular ring which is rotatably mounted on the non-orbiting scroll member and includes portions operative to open and close, one, two or more vent passages simultaneously. In one form a single actuator is provided which is operative to move the valving member preferably from an open reduced capacity position to a closed position and a return spring operates to return the valving member to a preferred open position. In another form, the return spring is omitted and the actuator operates to drive the valving member between the open and closed positions through application of either fluid pressure or electrically. In a second embodiment, the valving ring is supported on the main bearing housing and passages are provided therein which communicate with the compression chambers via openings in the end plate of the orbiting scroll member.
For any of these embodiments, a minimum number of parts are required to accomplish the capacity modulation. Further, the capacity modulation system of the present invention will preferably be designed such that the compressor will be in a reduced capacity mode at both start up and shut down. The reduced capacity starting mode reduces the required starting torque because the compressor is compressing a substantially smaller volume of refrigerant. This reduced starting torque enables use of a lower torque higher efficiency motor. Also, reduced capacity operation at shut down reduces the potential and degree of noise generating reverse rotation of the scrolls thereby enhancing customer satisfaction. Additionally, the system of the present invention is designed such that should the actuating system fail, the compressor will be able to continue operation in a reduced or modulated capacity mode. This is desirable because under normally encountered operating conditions, the compressor will spend most of its running time in the modulated or reduced capacity mode.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.